What he said. Sadly, I sort of treat the Cohort like this as well, giving control to the PC more than my own device. Keep a watchful eye though, that I do.The DM controls it, in so much that any interaction with the mount is pending the DM's approval, but otherwise, treat it as a normal mount. It will generally follow directions and help the companion/"owner" where it can, as intelligent mounts must be bonded/befriended/otherwise coerced into helping, and therefor have reasons to be generally helpful.